1. Field of the Invention
The present invention relates to a rotary connector, and particularly to a rotary connector having an alignment feature and/or an overcurrent protection feature.
2. Discussion of the Background
A rotary connector is used as a connector device for a flexible transmission medium that transfers electrical signals, optical signals, electric power, etc. between a stationary member and a rotating member rotating relatively to the stationary member within a limited range of rotational number. In this rotary connector, a flexible flat cable is housed in the form of a spiral connector within an annular space defined by a rotating case and a stationary case, which are combined for rotation. Alternatively, U.S. Pat. No. 5,310,356 assigned to The Furukawa Electric Co., Ltd discloses a flexible flat cable is housed in a rotary case in the form of stationary windings along the inside wall of the stationary member, then reversing direction via a U-shape turn, and continuing as rotating windings along the outside wall of the rotational member. The entire contents of U.S. Pat. No. 5,310,356 are incorporated herein by reference. Opposing ends of the flexible flat cable are connected to the rotating case and stationary case respectively, and the rotating case is allowed to rotate relatively to the stationary case as the flat cable is coiled and uncoiled simultaneously from the respective side walls of the rotary connector.
The rotary connector is typically required to be in a neutral position when mounted in a final assembly. The neutral position is usually a center position in the range of rotational movement of the rotary connector so that the rotary connector can be rotated the same number of rotations (i.e. angular rotational range) in both the clockwise and counterclockwise direction without damaging the flexible flat cable fixed to the stationary and rotary part of the rotary connector. That is, the neutral position allows the same number of functional rotations in either direction. In mounting the rotary connector in the steering apparatus of an automobile, for example, the steering wheel is adjusted to a straight-advance position as the neutral position connector is set into the steering apparatus. Thus, the steering wheel is free to operate the steering apparatus without causing a strain (or breaking) the flexible flat cable.
Because the rotary connector is provided as a subcomponent of a final assembly, such as a steering wheel assembly, the rotary connector is typically fixed in the neutral position until placed in the final assembly, where the rotary connector is made free to rotate in the assembly. Fixing in the neutral position is typically provided by a fixing pin having retaining hooks, called snap fits, that are removably mounted extending between mounting portions on the rotating and stationary cases, or by a seal that is pasted on both the cases. An example of a fixing mechanism is disclosed in U.S. Pat. No. 5,257,943, the entire content of which is incorporated herein by reference.
Conventional methods of fixing or sealing the rotary connector are problematic, however, in that it is difficult to verify that the connector is actually in the neutral position at the time of assembly. While the rotational and stationary part of the connector may have alignment marks that indicate the relative position of these parts when they are in the neutral position, because the rotational connector can make several complete rotations, the alignment marks may be aligned in positions other than the neutral position. Therefore, if the fixed or sealed neutral position is broken during transport of the rotary connector to the place of final assembly, for example, the neutral position cannot be found by using the alignment marks. Moreover, even if the fixed or sealed neutral position is not broken, it cannot be visually verified at final assembly that the rotary connector is actually in the alignment position corresponding to the neutral position.
Over current protection for the flexible flat cable has conventionally been provided by a fuse housed in a fuse box mounted on the final assembly such as a vehicle chassis. Such a fuse box is typically bulky and requires additional wiring from the rotary connector, which leads to additional material and assembly cost. Moreover, the fuse box may be accessible to an inexperienced user of the final assembly, which may lead to the wrong fuse being provided in the fuse box. Where the replaced fuse is rated lower than the proper fuse rating, premature blowing of the fuse may occur. More importantly, where the replaced fuse is rated higher than the proper fuse rating, excessive heat and even fire may result.